Pb-Free brass is used as a piping member. In addition, Pb-free filler metal is used for as a solder material. However, few evaluations of the solderability of a Pb-free filler metal applied to Pb-free brass have been conduct-ed. Therefore, in the present study, while assuming the soldering part of the piping member, a parallel two-piece plate test piece is proposed to create as simple a specimen shape as possible, and experiments were carried out. We conducted an experiment to evaluate the solderability using an X-ray transmission image for an observation evaluation. From the results of this experiment, it was found that the use of a transmission image is appropriate as an evaluation method. In addition, it was possible to classify the voids of the soldering part into four types. It was suggested that the occurrence of a spherical void, which is one of the four types of voids, is caused by the occurrence of bubbles created by the flux. Therefore, we investigated the occurrence of air bubbles using a field observation experiment. As a result, we were able to confirm the occurrence of bubbles during the soldering. In addition, it was possible to suppress the occurrence of air bubbles by using a dry flux that can reduce the amount of solvent in the flux. As a result of the solder experiment with the parallel two-piece plate specimen using a drying flux, the number of spherical voids appearing in the solder area decreased to almost zero.
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